1. Field of the Invention
The invention relates to improvements in flotation means for subsea wall risers; and, more particularly, to means for making such flotation means completely adjustable.
2. Description of the Prior Art
In U.S. Pat. No. 3,858,401 to Watkins, flotation is provided for a subsea well riser conduit run between a floating vessel provided with a source of compressed gas or air and a subsea well head. Such flotation means includes a plurality of open bottom buoyancy gas receiving chambers and means for mounting them about and along the riser conduits. Air or gas conduit means connected between the source of compressed gas and each of the chambers introduces gas in selectable amounts into the chamber, displacing water entrained therein out the open bottom of the chamber to provide a selectable amount of buoyancy to the riser conduit. Gas valve means are provided at one or more of the chambers. The gas valve means include associated float means for holding the valve means open when the water level is above a predetermined level in the associated chamber and for closing the valve when the water level falls below the level to avoid loss of gas out through the open bottom of the chambers. A restricted orifice is provided between each chamber and the gas conduit means to provide a generally equal distribution of gas to each chamber from the gas conduit. The opened bottom buoyancy chamber includes an annular airtight flange formed integrally of an extending radially outward from each of a plurality of riser conduit sections and a plurality of generally cylindrical airtight shells. Mounting means mount the shells about the riser conduit in an airtight and depending relationship to an associated annular flange to thereby provide airtight top and side walls to the open bottom chambers. A centralizer is provided at the bottom of each chamber to generally maintain the desired spacing between the shells and the conduit sections. The advantages of this flotation means over prior art systems is discussed in detail in the Watkins patent. However, it is desirable that the buoyancy in each chamber be adjustable so as to render the entire system completely adjustable. no such means are disclosed in the Watkins patent.